The present invention relates to apparatus for subjecting a material to electromagnetic waves. Such apparatus, hereinafter referred to as an "applicator", is typically used to treat a confined material, one at least of whose constituents is a dielectric in liquid, solid or even gaseous phase, with electromagnetic waves having a frequency above 1 MHz and preferably above 400 MHz, with a view to supplying it with energy.
Applicators of this type are used in the most varied fields, for example, the treatment of food products, the heating of insulating materials, plastics materials, concrete, rubber and ores, the effecting of polymerizations, desorptions, drying, separations or other physical and chemical actions or reactions which involve one of the constituents of the material or take place between the constituents of the latter.
Applicators using an antenna to radiate electromagnetic energy are known, for example, in high frequency electric ovens. In such an applicator, the antenna is fixed to one of the two extreme right sections of the applicator and radiates towards the corresponding right section of the material to be treated. Such an apparatus is satisfactory in the field of application for which it has been conceived, namely an oven concerned with heating a confined material, within the applicator, in a region whose transverse and longitudinal dimensions are appreciably of the same order.
On the other hand, it presents grave drawbacks in the case of elaborate industrial applicators, where one is concerned with inducing the aforementioned reactions by carefully proportioned contribution of electromagnetic energy, such as applicators used in the chemical industry. In this case, the dimensions of the applicator are imposed by the conditions of use, that of chemical engineering in the example mentioned. These conditions often involve an important relation between the longitudinal and transverse dimensions of the applicator: its section being most often circular, the latter looks like a true column whose height is equal to several times the diameter, in particular at least twice and generally at least four times.
In these conditions, the supplying of electromagnetic energy through the means of an antenna placed as indicated above leads to the major drawback of a preferential absorption of this energy in those areas of material to be treated which are nearest the antenna, and consequently to a rapid attenuation of the residual energy available for the treatment of the next areas. In order to supply the necessary minimal energy in the area furthest from the antenna, it is therefore necessary to provide an excess of energy in the nearest areas. This situation leads to overheating in these areas, if heating is the effect sought, or to the racings of reactions, with all the consequences that that implies, in the case of more elaborate industrial applicators.
It is an object of the present invention to reduce this grave drawback by ensuring for each right section of the applicator an identical contribution of electrical energy, whatever its longitudinal position within the applicator.